As is known, there are a variety of types of magnetic field sensing elements, including, but not limited to, Hall effect elements, magnetoresistance elements, and magnetotransistors. As is also known, there are different types of Hall effect elements, for example, planar Hall elements, vertical Hall elements, and circular Hall elements. As is also known, there are different types of magnetoresistance elements, for example, anisotropic magnetoresistance (AMR) elements, giant magnetoresistance (GMR) elements, tunneling magnetoresistance (TMR) elements, Indium antimonide (InSb) elements, and magnetic tunnel junction (MTJ) elements.
Hall effect elements generate an output voltage proportional to a magnetic field. In contrast, magnetoresistance elements change resistance in proportion to a magnetic field. In a circuit, an electrical current can be directed through the magnetoresistance element, thereby generating a voltage output signal proportional to the magnetic field.
Magnetic field sensors, which use magnetic field sensing elements, are used in a variety of applications, including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch (also referred to herein as a proximity detector) that senses the proximity of a ferromagnetic or magnetic object, a rotation detector that senses passing ferromagnetic articles, for example, gear teeth, and a magnetic field sensor that senses a magnetic field density of a magnetic field. Particular magnetic field sensor arrangements are used as examples herein. However, the circuits and techniques described herein apply also to any magnetic field sensor.
As is known, some integrated circuits have internal built-in self-test (BIST) capabilities. A built-in self-test is a function that can verify all or a portion of the internal functionality of an integrated circuit. Some types of integrated circuits have built-in self-test circuits built directly onto the integrated circuit die. Typically, the built-in self-test is activated by external means, for example, a signal communicated from outside the integrated circuit to dedicated pins or ports on the integrated circuit. For example, an integrated circuit that has a memory portion can include a built-in self-test circuit, which can be activated by a self-test signal communicated from outside the integrated circuit. The built-in self-test circuit can test the memory portion of the integrated circuit in response to the self-test signal.
Conventional built-in self-test circuits used in magnetic field sensors tend not to test the magnetic field sensing element used in the magnetic field sensor. Conventional built-in self-test circuits also tend not to test all of the circuits with a magnetic field sensor.
Some magnetic field sensors employ self-calibration techniques, for example, by locally generating a calibration magnetic field with a coil or the like, measuring a signal resulting from the calibration magnetic field, and feeding back a signal related to the resulting signal to control a gain of the magnetic field sensor. Several self-calibration arrangements are shown and described in U.S. Pat. No. 7,923,996, entitled “Magnetic Field Sensor With Automatic Sensitivity Adjustment,” issued 26, 2008, and assigned to the assignee of the present invention. Also U.S. patent application Ser. No. 12/840,324, entitled “Circuits and Methods For Generating A Diagnostic Mode Of Operation In A Magnetic Field Sensor,” filed Jul. 21, 2010, U.S. patent application Ser. No. 12/706,318, entitled “Circuits and Methods for Generating a Self-Test of a Magnetic Field Sensor,” filed Feb. 16, 2010, and U.S. patent application Ser. No. 13/095,371, entitled “Circuits and Methods for Self-Testing or Self-Calibrating a Magnetic Field Sensor,” filed Apr. 27, 2011, each assigned to the assignee of the present invention, teach various arrangements of coils and conductors disposed proximate to magnetic field sensing elements and used to generate self-test magnetic fields. The above patent and applications also teach various multiplexing arrangements. These applications and patent, and all other patent applications and patents described herein, are incorporated by reference herein in their entirety.
Typically, a self-test or a self-calibration of a magnetic field sensor takes place at a single rate or during a single predetermined time period (i.e., with a single bandwidth). In some applications, this single rate, when used for self-calibration, may result in the magnetic field sensor being inaccurate for a substantial amount of time following a power up of the magnetic field sensor. However, speeding up the self-test or the self-calibration, i.e., increasing the bandwidth of the self-calibration would result in the magnetic field sensor being less accurate and having a higher output noise level.
Also typically, self-test and/or self-calibration of the magnetic field sensor must be performed when the magnetic field sensor is not sensing a sensed magnetic field, i.e., when the magnetic field sensor is not operating in its regular sensing mode in which it is sensing an external magnetic field.
It would be desirable to provide built in self-test and/or self-calibration circuits and techniques in a magnetic field sensor that allow the self-test and self-calibration functions to test and calibrate the magnetic field sensor at a fast rate (i.e., within a short time period) while not reducing resolution and while not increasing output noise level.
It would also be desirable to provide built in self-test and/or self-calibration circuits and techniques in a magnetic field sensor that allow the self-test and self-calibration to occur while the magnetic field sensor is operating in its regular sensing mode.
It would also be desirable to provide built in self-test circuits and techniques in a magnetic field sensor that allow the self-test function to test a magnetic field sensing element used within the magnetic field sensor.
It would also be desirable to provide built in self-test circuits and techniques in a magnetic field sensor that allow the self-test all of the circuits within the magnetic field sensor.